Various motion systems may be used in flight simulators or driving simulators. Notably, mobilization systems are used in helicopter or aircraft flight simulators. They meet qualification criteria defined by certification bodies, notably the FAA, the acronym standing for the expression Federal Aviation Administration and the equivalent in Europe of the JAA, the acronym standing for the expression Joint Aviation Authorities.
The invention can notably be applied to simulators meeting FFS level B qualification criteria, the acronym standing for the expression Full Flight Simulator level B, i.e. flight simulator of level B. This type of simulator is increasingly prized by customers on account notably of their small proportions relative to simulators of FFS level D type. The invention can also be applied to simulators meeting FFS level D qualification criteria.
The best known prior art in regard to mobile platforms for simulators is a Stewart platform. The concept of the Stewart platform is based on the use of a hexapod positioner allowing motion with six degrees of freedom. Stewart mobile platforms are notably used for flight simulators, according to a design by K. Cappel. The type of motion of these platforms forms part of the family of parallel robots.
Several possible motorizations exist for moving a hexapod according to the prior art:                hydraulic rams, mainly used to mobilize loads of greater than about fourteen tonnes;        screw-type electric rams, for loads of less than about fourteen tonnes;        pneumatic systems for small loads, for example less than five hundred kilos.        
The existing motorizations, making it possible to move a hexapod according to the prior art, are products having a fixed configuration for a given application. For example to change the travel of a ram, it is necessary to place a stop inside the ram or to elongate the length of the screw. Therefore, modifying the length of the ram gives rise to a new design of the ram, a revalidation and a re-investigation of the kinematics and of the geometry of the hexapod.
The existing products do not therefore make it possible to carry out simple adaptations of geometry, as a function of customer requests, in regard to simulators notably. Moreover, these products are produced in small quantities and are therefore very expensive.
In the case of hexapods with electric rams, the level of vibration and the noise are more significant than with hydraulic hexapods, and this may disturb pilot training. This phenomenon is due mainly to the recycled motions of the balls on the screw or to the rollers propelled at high speed on the screw.
Moreover, in the case of a hexapod according to the prior art, the integration of safety elements is very constraining, notably:                The return to a horizontal stable position, in the case of a power outage or an electrical control fault, so as to facilitate the exit of the crew, requires an ancillary backup power supply source. This type of backup power supply is expensive both in respect of its purchase and its servicing.        In the case of failure of the command and control systems, shock absorbers must be integrated to avoid fierce decelerations at the end of the travel, because of the presence of the screw; they are designed and certified specially for this type of application and are therefore much more expensive than the shock absorbers chosen from the catalogues of industry suppliers.        